It is known in the weaving art to project a weft strand through the shed of a loom by means of a nozzle situated adjacent one side of the shed and capable of emitting into the shed a stream or jet of pressurized gas, typically air, for entraining the strand therein, the strand preferably being delivered for this purpose directly into the base of the nozzle. It is also known to associate with such a nozzle a weft guidance tube made up of an elongated array of closely spaced elements or segments having their lower ends mounted on the lay and defining with their free ends an interrupted or "porous" internal channel-like passageway extending through the shed to receive the air-projected strand. The elements as well as the passageway itself can take various shapes but a preferred shape for the free end is annular to give a generally tubular passageway. The free end of each element is provided with a slot-like opening from the internal passageway situated at a common peripheral point on all the elements through which the inserted strand can escape laterally from the passageway.
In prior art air insertion systems of this type, the array of segments or elements constituting the interrupted guidance tube are mounted in fixed position on the lay of the loom forwardly of the reed in such a location that as the lay swings forwardly to impact the reed against the fell of the fabric, the guidance tube elements are carried bodily below and outside of the shed to an inoperative position clear of the fell of the fabric which does not interfere with the beat up action of the reed. The inserted weft thread is naturally restrained from leaving the shed as the guidance tube is withdrawn to inoperative position outside the shed, due to the fact that the inserted weft extends across a multiplicity of warp strands and is prevented thereby from further lateral movement therebeyond. The slot-like opening in the guidance tube element permits the inserted weft to escape from the interior of the passageway formed by the elements as the latter drop below the floor of the shed, and to remain within the shed despite the withdrawal of the guidance tube therefrom.
Thus, the removal of the inserted weft from the guidance tube elements has up to now been a passive response of the inserted weft to the rocking motion of the lay, dependent upon the position of the guidance tube elements upon the lay, the effective arc of the lay and the initial orientation of the lay relative to some reference point, as to the point in the loom operating cycle at which the inserted weft egresses from the guidance tube elements. Since the lay is necessarily narrow in the warpwise direction, the possibility of warpwise adjustment of the position of the guidance tube array on the lay is insignificantly small, practically speaking, and the only way available to the prior art of adjusting the timing in the operative cycle of the egress of the inserted weft from the guidance tube is by changing the overall orientation angle of the lay, i.e., the angle of the lay supports at dead center. Such a change, however, requires a relocation of the lay pivot axis, an alteration in the length of the lay supports or both and neither can normally be accomplished without effecting a complete redesign of the loom in question. It would be desirable to provide greater flexibility in the air insertion system as to the timing of the removal of the inserted weft from the guidance tube array, as well as to achieve a direct or positive, rather than merely passive, withdrawal of the inserted weft from the guidance array in a positive fashion not dependent upon any blocking action of the warp threads which introduces the possibility of such threads becoming damaged.